Multiple Olympic champion Usain Bolt has taken a step forward in his preparations as he bids to defend his world titles this season and remains unfazed by the challenge from sprinter Justin Gatlin.

Multiple Olympic champion Usain Bolt has taken a step forward in his preparations as he bids to defend his world titles this season and remains unfazed by the challenge from sprinter Justin Gatlin.

American Gatlin dominated the Diamond League 2014, running 9.77 seconds and 19.68 seconds in 100 metres and 200 metres. Bolt's coach Glen Mills said the sprinter had stepped up his preparations since running 46.37 seconds over 400m in Kingston, Jamaica in March.

"Usain has made significant strides since the last time you saw him," Mills was quoted as saying by BBC.

Bolt ran only three races last year but said he is optimistic about the current season.

"I want to run really fast this season so I'm working on it. I'm happy with where I'm at. I'm doing a lot of work leading up to this first run in Brazil in April - that's the focus and that's what we're working towards," the 28-year-old said.

Bolt will bid for a third 100m gold and a fourth 200m gold in succession at August's World Championships in Beijing.

Gatlin, 33, won the 100m Olympic gold in 2004 and the World Championship gold in 2005.

"We take all competitors with a level of seriousness. But the truth of the matter is Usain at his best doesn't have much to worry about," Mills said.